Xen users - Feb 2012 - how to use multi-layer image files to create VMs

Hi,
 
As we know, qcow/qcow2 format image files could be used to create VMs and a
qcow/qcow2 format image file could be based on some image file, which compose a
two-layer-image-file structure.Thus I would like to create a
multi-layer-image-file structure.In this multi-layer-image-file structure one
image file is based on another  and the image files are like a stack.However
after I try a lot of times,I could not create VMs successfully.Who can tell me
which format I should choose and how to configure the disk in the XXX.hvm
configure file?
Thanks.
 
hxk

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2012/2/16 hxkhust <hxkhust@126.com>:
> Hi,
>
> As we know, qcow/qcow2 format image files could be used to create VMs and
> a qcow/qcow2 format image file could be based on some image file, which
> compose a two-layer-image-file structure.Thus I would like to create a
> multi-layer-image-file structure.In this multi-layer-image-file structure
> one image file is based on another  and the image files are like a
> stack.However after I try a lot of times,I could not create VMs
> successfully.Who can tell me which format I should choose and how to
> configure the disk in the XXX.hvm configure file?
> Thanks.

In short: I''d say don''t bother. It''s too much effort
for what it''s worth.

Newer versions of Xen can use blktap support if the kernel has it
(which is not upstream, so it''s unlikely you have it), or it can use
qemu emulation (which is dead slow). I wouldn''t recommend this
approach.

I recommend you do this instead:
(1) use xenserver, which implements VHD disks but stores the data in LVM. OR
(2) use a separate server as storage, put openinidiana + nappit on it,
and export the storage as iscsi to your xen dom0. That way you can
manage snapshot/clones using zfs from the storage server side. OR
(3) same as (2), but the storage server is actually just another domU.
The problem with this approach is that you need to make sure this domU
is started and functional before other domUs (possible, but requires
some effort).
(4) use ubuntu, install zfsonlinux, and use zvols as backing store.
There are some tuning you need to do to get acceptable performance
(e.g. increase number of zvol threads), but performance-wise it should
be somewhat similar or better to (3).

-- 
Fajar